1. Field of the Invention
This invention relates generally to organoborane amine complex initiator systems and, more specifically, to systems in which the complex is carried in a 1,4-dioxo-2-butene-functional material. The invention further relates to polymerizable compositions made therewith, particularly two-part acrylic adhesive compositions. The adhesive compositions have excellent adhesion to a variety of substrates, especially low surface energy polymers.
2. Description of the Related Art
An efficient, effective means for adhesively bonding low surface energy plastic substrates such as polyethylene, polypropylene and polytetrafluoroethylene (e.g., TEFLON) has long been sought. The difficulties in adhesively bonding these materials are well known. See, for example, "Adhesion Problems at Polymer Surfaces" by D. M. Brewis that appeared in Progress in Rubber and Plastic Technology, volume 1, page 1 (1985).
The conventional approaches often use complex and costly substrate surface preparation techniques such as flame treatment, corona discharge, plasma treatment, oxidation by ozone or oxidizing acids, and sputter etching. Alternatively, the substrate surface may be primed by coating it with a high surface energy material. However, to achieve adequate adhesion of the primer, it may be necessary to first use the surface preparation techniques described above. All of these techniques are well known, as reported in Treatise on Adhesion and Adhesives (J. D. Minford, editor, Marcel Dekker, 1991, New York, volume 7, pages 333 to 435). The known approaches are frequently customized for use with specific substrates. As a result, they may not be useful for bonding low surface energy plastic substrates generally.
Moreover, the complexity and cost of the presently known approaches do not render them particularly suitable for use by the retail consumer (e.g., home repairs, do-it-yourselfers, etc.) or in low volume operations. One vexing problem is the repair of many inexpensive everyday household articles that are made of polyethylene, polypropylene or polystyrene such as trash baskets, laundry baskets and toys.
Consequently, there has been a considerable and long felt need for a simple, easy to use adhesive that can readily bond a wide variety of substrates, especially low surface energy materials, such as polyethylene, polypropylene and polytetrafluoroethylene, without requiring complicated surface preparation, priming and the like.
While an adhesive that can bond low surface energy plastics is certainly advantageous, the commercial utility of such an adhesive would be enhanced if the components thereof could be combined in a convenient mix ratio. This would permit facile application of the adhesive using conventional adhesive dispensers without the need for laborious hand weighing and mixing of the different components. However, the convenient mix ratio should not come at the expense of significantly reduced storage stability or performance. Thus, there is not only a need for an adhesive that can bond low surface energy plastics, but a need for such an adhesive that can be readily blended in a convenient mix ratio.
It may be desirable for such adhesives to possess other attributes. For example, polymerizable acrylic adhesives are often associated with a strong and unpleasant odor. While not affecting performance, the odor may discourage some people from using these adhesives and encourage them to select other, perhaps more expensive, alternatives. In addition, for certain situations, it may be helpful to have a readily crosslinkable adhesive to form the high strength adhesive bonds demanded in structural bonding applications.
In still other settings it may be desirable for the adhesive to display an extended shelf-life; that is, to remain stable at room temperature for an extended period of time. In this manner, special storage conditions such as refrigeration can be avoided without substantially reducing the storage life of the product. The likelihood that product would need to be discarded because it has been stored beyond its shelf-life would also be reduced. Similarly, stability at elevated temperatures (for example, in excess of 150.degree. F.) for an extended period of time may also be desirable if the adhesive will be exposed to such temperatures prior to use. This could occur during shipping or if the adhesives are inventoried in warehouses or other storage facilities located in hot weather climates but which are not air conditioned.
Some adhesive compositions are subject to yellowing or other discoloration upon exposure to heat or ultraviolet radiation. This can be undesirable if the adhesive composition is used to bond transparent or translucent substrates or if the adhesive bond line will otherwise be visible. For such applications an adhesive composition that remains white or opaque upon exposure to heat and ultraviolet radiation may be preferred.
As explained more fully hereinbelow, organoborane amine complex initiator systems and related compositions of the invention (which include 1,4-dioxo-2-butene-functional material and acrylic monomer that can polymerize to acrylic adhesives) can address these demands and offer many other advantages.
Organoboranes such as tributylborane and triethylborane have been reported to initiate and catalyze the polymerization of vinyl monomers (see, for example, G. S. Kolesnikov et al., Bull. Acad. Sci. USSR, Div. Chem. Sci. 1957, p. 653, J. Furakawa et al., Journal of Polymer Science, volume 26, issue 113, p. 234, 1957; and J. Furakawa et al., Journal of Polymer Science, volume 28, issue 116, 1958). The organoborane compounds of the type described in these references are known to be quite pyrophoric in air which complicates facile use.
Chemical Abstracts No. 134385q (volume 80, 1974) "Bonding Polyolefin or Vinyl Polymers" reports that a mixture of 10 parts methyl methacrylate, 0.2 part tributylborane, and 10 parts poly(methylmethacrylate) was used to bond polyethylene, polypropylene and poly(vinyl acetate) rods.
U.S. Pat. No. 3,275,611 to E. H. Mottus et al. discloses a process for polymerizing olefinic compounds (e.g., methacrylate monomers) with a catalyst comprising an organoboron compound, a peroxygen compound, and an amine. The organoboron compound and the amine may be added to the reaction mixture separately or they may be added as a preformed complex.
British Patent Specification No. 1,113,722 "Aerobically Polymerisable Compositions," published May 15, 1968 discloses the polymerization of acrylate monomers through the use of a free-radical catalyst (e.g., peroxides) and triarylborane complexes having the general formula (R).sub.3 B-Am wherein R is an aryl radical and Am is an amine. The resulting compositions are reportedly useful as adhesives.
Chemical Abstracts No. 88532r (volume 73, 1970) "Dental Self-curing Resin" and the full text paper to which it refers report that tributylborane can be made stable in air by complexing it with ammonia or certain amines and that the tributylborane can be reactivated with an amine acceptor such as an isocyanate, an acid chloride, a sulfonyl chloride, or acetic acid anhydride. As a result, the complex can be used to polymerize blends of methyl methacrylate and poly(methylmethacrylate) to provide a dental adhesive.
U.S. Pat. No. 4,638,092 to Ritter discloses organic boron polymers and their use to start polymerizations. The organo-boron compounds are characterized by the fact that the boron-containing radicals are connected to an organic polymer matrix that is largely non-reactive when exposed to atmospheric oxygen. The polymer matrix can be obtained by polymerizing diolefins, by copolymerizing diolefins with alpha-olefins, or by the polycondensation of diols or diamines with dicarboxylic acids containing olefin groups such as maleic acid and fumaric acid. U.S. Pat. No. 4,639,498, also to Ritter, describes the use of the organo-boron compounds to provide two component adhesives.
A series of patents issued to Skoultchi or Skoultchi et al. (U.S. Pat. Nos.: 5,106,928; 5,143,884; 5,286,821; 5,3 10,835; and 5,376,746) disclose a two-part initiator system that is reportedly useful in acrylic adhesive compositions, especially elastomeric acrylic adhesives. The first part of the two-part system includes a stable organoborane amine complex and the second part includes a destabilizer or activator such as an organic acid or an aldehyde.
A series of patents issued to Zharov et al. (U.S. Pat. Nos.: 5,539,070; 5,690,780; and 5,691,065) disclose a polymerizable acrylic composition that comprises at least one acrylic monomer, an effective amount of certain organoborane amine complexes, and an effective amount of an acid for initiating polymerization of the acrylic monomer. The acrylic composition is especially useful as an acrylic adhesive for bonding low surface energy polymers.
A series of patents issued to Pocius et al. (U.S. Pat. Nos.: 5,616,796; 5,684,102; and 5,795,657) disclose polymerizable acrylic compositions that comprise acrylic monomer, organoborane polyamine complex, and a material reactive with amine. Polymerizable acrylic monomer compositions useful as adhesives for bonding low surface energy polymers can be prepared. The polyamine is the reaction product of a diprimary amine-terminated material, and a material having at least two groups reactive with primary amine.
U.S. Pat. Nos. 5,621,143, 5,681,910 and 5,718,977 to Pocius disclose polymerizable acrylic monomer compositions that comprise acrylic monomer, organoborane polyoxyalkylene polyamine complex, and an amine reactive compound. The compositions are useful as adhesives for bonding low surface energy polymers.
In U.S. Pat. No. 5,686,544 Pocius discloses a polyurethane/polyurea acrylic adhesive composition that has exceptionally good adhesion to low surface energy polymers. The adhesive composition comprises acrylic monomer, organoborane polyamine complex, polyol and polyisocyanate.